If I have two strings of equalities within the same align or alignat environment, and the first one is long enough to need two lines, I would want the result to look like

rather than

Is there a way to do this? I suppose it can be done with an array, but I thought either align or alignat would be able to handle this. I get garbage results like these:

\begin{alignat}{3}

&F_k &=(f\chi_E)^{-1}(v_k)=\{x\in X|f(x)\chi_E(x)=v_k\}=\{x\in X|f(x)=v_k\}\cap E\\

&&=f^{-1}(v_k)\cap E=E_k\cap E\in\Sigma,\\

&\mu\big(F_k)=\mu(E_k\cap E)\leq\mu(E_k)<\infty.

\end{alignat}

\begin{alignat}{4}

&F_k && =(f\chi_E)^{-1}(v_k) =\{x\in X|f(x)\chi_E(x)=v_k\}=\{x\in X|f(x)=v_k\}\cap E\\

&&&=f^{-1}(v_k)\cap E=E_k\cap E\in\Sigma,\\

&\mu\big(F_k)=\mu(E_k\cap E)\leq\mu(E_k)<\infty.

\end{alignat}